Right from the opening frames of what some people will call a psychological horror film and others will label a dark comedy, no viewers are going to be absolutely sure about what they’re watching. Until it’s time for them to understand. First-time writer-director Cory Finley has spent the last few years churning out Off-Broadway and Off Off-Broadway plays, and has now turned his play “Thoroughbred” into the film “Thoroughbreds.”

His story tells of two young women — once friends, later ex-friends, now thrown back into each other’s orbit — who come from wealth, but both appear to be damaged goods. He takes his audience on an emotional ride that’s rife with sometimes uncomfortable humor (Are we supposed to laugh? Will strangers sitting next to us in the dark judge us harshly for laughing? Note: I laughed, nervously and often.).

The film’s opening shot is long and wordless. It’s of Amanda (Olivia Cooke, from “Me and Earl and the Dying Girl”) and a horse, staring at each other. The camera reveals a large knife nearby. But before any of that can sink in, the scene shifts to Amanda, sometime later, being dropped off at a huge home to visit with Lily (Anya Taylor-Joy, from “Split”). They’re the old friends who are now back together. But this isn’t a social visit. The aloof Amanda is there to be tutored by Lily, who treats all of this as business, which it is, since she’s being paid to do it.

That silent passage between Amanda and the horse turns out to be the first of many in the film, and the two young actresses are terrific in getting across what they’re thinking (or not thinking) via facial expressions. Add to that some uneasy body language on the part of Lily, especially when her creepy stepdad Mark (Paul Sparks, from “Boardwalk Empire”) comes around, lurking and watching, kind of like Donald Trump behind Hillary Clinton on the debate stage.

“You hate him,” states Amanda to Lily, which increases the obvious tension between the two women, but they manage to get past that stage, eventually settling down on a couch to watch old movies.

From there, this tale of misery among the affluent shoots off into myriad directions that will keep viewers off-balance and on edge, though there are plenty of clues offered up to hint at the so many things that are wrong.

Lily’s mom, only spoken of at first, is finally seen in the basement, basking, likely against her will, in a tanning bed because, “Mark likes a little color on me.” Mark is later proven to be a total jerk, and a threatening presence in her life. Lily has a possibly sinister secret in her past, as might Amanda, who casually admits to Lily that she has “no feelings; I can’t feel joy or guilt.”

When the slightly older Tim (the late Anton Yelchin in a superb performance), a kind of shady, drug-dealing fellow, is introduced, it becomes hard to choose who is the most unsettling character in the film — Tim, Mark, or Amanda.

By now, the film’s many silences have been complemented by passages of big, loud, percussive music, as well as by industrial-like sounds that are reminiscent of the noises heard throughout David Lynch’s “Eraserhead.” On top of that, a quietly dizzying uncertainty sets in regarding Lily and Amanda. Is one of them manipulating the other? Are they both suicidal? Do they really know what they’re doing when they approach Tim with a money-making proposition, then hand him a pistol?

There are repeated instance of people going into blank, expressionless mode, that horse from the opening frames gets its own unfortunate story (told in passionless manner by Amanda), and the nerve-wracking atmosphere gets extreme when more and more awful things happen, almost all of them off-camera. Once caught up in it, viewers will stay under the film’s spell until the misguided coda which tries to clean things up a bit, when they ought to have been left dirty.

— Ed Symkus writes about movies for More Content Now. He can be reached at esymkus@rcn.com.